Radiation therapy involves medical procedures that selectively expose certain areas of a human body, such as cancerous tumors, to doses of radiation. The purpose of the radiation therapy is to irradiate the targeted biological tissue such that undesirable tissue is destroyed. Radiation has also been-used to obtain image of tissue for diagnostic or treatment purposes.
During delivery of radiation towards a patient, it may be desirable to ensure that a target receiving the radiation remains fixed in position relative to a certain coordinate system. Also, it may be desirable to know the position of a patient support supporting the patient relative to a certain coordinate system.